Structural Studies of Polyesters. II. Far-Infrared Spectra of Aliphatic Polyesters: Comparison with α-Polyamides

Abstract

Polarized far-infrared spectra of aliphatic polyesters [–(CH2)z–CO–O–O]n with z = 1, 2, and 5 (z = 4, nonpolarized) and α-polyamide (nylon 6 and its N-deuteroderivative) have been measured in the region up to 80 cm−1. All these polymers have essentially planar zigzag conformations. The normal vibrations of these polymers were calculated for the far-infrared regions by using the Urey–Bradley force field with some modifications. For the series of polyesters, several far-infrared bands were found to appear systematically at nearly the same positions with similar intensities. The similarities between these series of bands of the polyesters and those of polyamides were interpreted from the point of view of the normal modes of vibrations.

Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics

“…In principle, the number of absorption bands (one or perhaps more) at these frequencies cannot be inferred reliably taking into account only the absorption spectrum in this spectral vicinity. However, the rather abrupt change in the slope of the refractive index found in this spectral range suggests the presence of two resonant modes, in good agreement with the reports of FTIR measurements for this frequency range [34,35]. These two peaks centered at 8.82 THz and 9.51 THz are fingerprints of the two different structures of PA6: respectively the α-PA6 with the CONH group coplanar to the methylene group planes and the γ-PA6 which has the CONH group perpendicular to those planes.…”

“…Usually both forms are present in different degrees of disorder, as reported in [33,34]. The presence of the α-form in our PA6 sample is substantiated by the pronounced shoulder at 6.63 THz [33,34] previously attributed to a torsional vibration mode of the methylene chain [35]. At even higher frequencies one can identify the band centered at 13.4 THz (Fig.…”

“…In contrast to previous studies performed using FTIR [26][27][28][29][31][32][33][34][35], THz TDS provides a unique access to both the real and the imaginary part of the dielectric function. Besides, unlike FTIR, THz TDS is an ultrafast technique which can be easily used in pump-probe arrangement, thus directly yielding the dynamics of the ultra-broadband THz response of material of interest under ultrafast illumination.…”

“…6(b)). The latter has been reported and identified in the literature as the bending of the CH 2 chain coupled with the in-plane bending of the C = O group [35]. Further infrared-active vibrational modes are expected beyond our frequency window, such as the bands centered around 15.69 THz and 17.37 THz [35].…”

Ion complexation in nonactin, monactin, and dinactin: A Raman spectroscopic study

“…This mode and the neighboring 405-410 cm-' band could also represent 0-C-C skeletal bend. 15 The 443 cm-l band is too weak to be observed in the uncomplexed nactins, which is consistent with the observed enhancement of the intensity of the other ester peaks (520, 867,1720 cm-I) upon complexation.…”